Had an S320 converted around 9 months ago, more or less as soon after the conversion was completed I began getting random stalls when braking at junctions etc, engine would rock at low revs but only after having been driven a while then when coming to a stop, also whenever I go to kick down to overtake it throws an Engine Management light up and starts running on 4 or 5 cylinders so quite roughly, and the fault is always Cylinder one misfire, I rang the fitter and he said if its doing it on petrol then its something on the petrol side so nothing to do with his installation? Iv'e had all the plugs changed new air filters, but although this seemed to help the problem is now getting worse, Iv'e noticed that if I am driving down a steep hill to a junction at the bottom the engine will run really roughly when I come to a stop and behaves like its misfiring but then after around 30secs it will calm down, seems to be ok going uphill, anyone have any ideas what this might be?

Do the problems happen on either fuel? None of this happened before the conversion? Were the plugs changed at time of conversion? Did the faults start just after the plugs were changed?

Simon

Hi Simon

The faults seem to be present on both fuels but more so on LPG , no problems prior to the installation of the LPG system its BRC by the way, it began playing up on the first day after the installation, so I changed the plugs only because I wanted to see if the problem was the plugs but it wasn't, changed air filters as well, I do need to get the LPG side serviced though but it isn't the need for a service that has caused this problem since its been there since day one it just getting worse now and its there all the time so might be easier to diagnose the problem?

Did it play up on petrol straight after installation? Would be a bit of a coincidence for the plugs to wear enough to make such a difference during only the time the installer had it... Wouldn't have suspected plugs, but now since you changed them you could have used a different type / gap / or a new plug could be faulty?

Best to start with the basics, and if you can be very specific about when problems occurred on both fuels relative to when work was done it could save time and the need to ask some of the basic questions.

Did it play up on petrol straight after installation? Would be a bit of a coincidence for the plugs to wear enough to make such a difference during only the time the installer had it... Wouldn't have suspected plugs, but now since you changed them you could have used a different type / gap / or a new plug could be faulty?

Best to start with the basics, and if you can be very specific about when problems occurred on both fuels relative to when work was done it could save time and the need to ask some of the basic questions.

Simon

I use the car every day cover around 1k miles a week, always on Gas, only ran it a couple of times on petrol after the fault appeared, its less pronounced on petrol? driving down hill to a junction always seems to result in the rough running when I come to a stop, it happen on the flat too, but going down hill really make it worse which is a bit baffling?

I have been researching it a little and people are saying the MAF Sensor or even the Crank Angle Sensor? something else I noticed was after I had taken the car into my local garage for a service they didn't quite fit the Air Filter housing back onto the metal riser (that gives the LPG Injectors clearance under the air filter) above the MAF sensor, doing this caused the problem of stalling to be far more pronounced, re-seating the filter housing onto the riser properly, helped a lot, so could this point to it being a MAF sensor issue?

Less pronounced on petrol implies the situation still occurs on petrol, which could point to a general vehicle problem (none LPG related) or could point to a fuel trim issue caused by LPG calibration. A general vehicle problem will often be exagerated when running on LPG because the mixture must be correct to more extend than when running on petrol and LPG ignition temp is higher. Proximity of LPG injectors to air filter housing could mean that when the airfilter was fitted differently it pushed against LPG injectors and could cause pipes between LPG injectors and manifold to kink. If your LPG system was calibrated (in a certain way) while the MAF sensor wasn't working properly, and then you corrected the MAF sensor problem, it might run worse on LPG after you sorted the MAF sensor issue. A lot of vehicle problems could point to crank sensor and MAF sensor issues, but again wouldn't it be a coincidence for a sensor to go wrong while you were having the LPG system fitted... There'd be nothing baffling to an engine running poorly going downhill (on over-run) on LPG, would be an indicator to me that calibration was off at very low loads and/or LPG injectors were being tasked with working below minimum pulse duration for which they can accurately meter fuel, and/or LPG ECU invoked a minimum LPG injector pulse duration (which would mean over-run would be rich).

With those sorts of iffs and buts you might as well bring it in to me, or ask your installer to re-consider the likelihood of coincidence of such faults occurring on petrol too at around the time you had the LPG system fitted. Such coincidences do occur, I converted a BMW in January and the crank sensor went on it a fortnight later, before I'd seen the car following the fault I too thought I must have caused the problem so met the owner half way between me and London. Your installer needs to be less quick to rule out his work as the cause of the problem, he should at least have a look instead of fobbing you off.

Less pronounced on petrol implies the situation still occurs on petrol, which could point to a general vehicle problem (none LPG related) or could point to a fuel trim issue caused by LPG calibration. A general vehicle problem will often be exagerated when running on LPG because the mixture must be correct to more extend than when running on petrol and LPG ignition temp is higher. Proximity of LPG injectors to air filter housing could mean that when the airfilter was fitted differently it pushed against LPG injectors and could cause pipes between LPG injectors and manifold to kink. If your LPG system was calibrated (in a certain way) while the MAF sensor wasn't working properly, and then you corrected the MAF sensor problem, it might run worse on LPG after you sorted the MAF sensor issue. A lot of vehicle problems could point to crank sensor and MAF sensor issues, but again wouldn't it be a coincidence for a sensor to go wrong while you were having the LPG system fitted... There'd be nothing baffling to an engine running poorly going downhill (on over-run) on LPG, would be an indicator to me that calibration was off at very low loads and/or LPG injectors were being tasked with working below minimum pulse duration for which they can accurately meter fuel, and/or LPG ECU invoked a minimum LPG injector pulse duration (which would mean over-run would be rich).

With those sorts of iffs and buts you might as well bring it in to me, or ask your installer to re-consider the likelihood of coincidence of such faults occurring on petrol too at around the time you had the LPG system fitted. Such coincidences do occur, I converted a BMW in January and the crank sensor went on it a fortnight later, before I'd seen the car following the fault I too thought I must have caused the problem so met the owner half way between me and London. Your installer needs to be less quick to rule out his work as the cause of the problem, he should at least have a look instead of fobbing you off.

Simon

Hi Simon

Yes its all guess work at the moment, like I mentioned before this is a working vehicle but I need to find time to travel down to you to let you have a look at it, you can service the Gas side at the same time if you wish, its overdue, been putting it off until I could locate the cause of the rough running and stalling problems, the cutting out is the most worrying part, it tends to just cut out at junctions usually after driving down hill, but not every time? you will have to let me know when you are available to have a look at the vehicle?

As you've implied, it won't be need of a service that is causing the problem. Cutting out at junctions and after driving downhill would point to incorrect fuelling when the engine is on low load / over-run, I'll certainly be able to prevent that.

Very busy this week coming converting 2 vehicles and repairing several others but I could see you early next week (later next week I'll be v busy again).

Have dropped it off at my local garage the stalling is getting a bit too frequent, cant go for kick down either to overtake, since this throws up a misfire on Cylinder one and then engine runs on reduced cylinders until the code is cleared, asked them to look at the MAF sensor and Crank angle sensor, needed the back brakes doing so just gave them a list see if they can help matters, failing this it can really only be something on the Gas side?

Hope your local garage are good at sussing the cause behind your types of symptoms, a lot of garages could do pretty major stuff like change a clutch no problem but resort to expensive guesswork when it comes to this type of fault.

Could be as simple as dodgy LPG system calibration throwing fuel trims off, or could be something like a manifold vacuum leak, broken wire or lambda probe. Some types of faults could have been present before you went for conversion but without necessarily showing any symptoms, then if the installer clears certain fault codes this can reset fuel trims and with the fault present the trims wouldn't be re-learned... I.e. Clearing fault codes without fixing the fault can cause worse drive-ability, so it's possible that the main thing the installer got wrong was just not noticing or addressing an existing vehicle fault. So, this is a bit in their defence, but I would still guess they messed something up!

I suspect the reply from the garage will be that it's the gas system that is causing the problem. They don't understand it and unless the cause is blindingly obvious, it must be down to this extra stuff that's been tacked on is the way they will look at it.

Well the garage just got back to me, they have found a corroded HT lead that snapped off as they began looking at the HT leads, said it was all green and corroded, they have ordered some HT leads and some coil packs to test everything out, they usually only fit what is needed and send everything else back, thats why I like using them, will update this thread later with the verdict?

Well the Garage fitted new HT leads and a single coil pack, vehicle seems to have developed several more Horses under the Bonnet, kick down does not cause an eml light to appear any longer, the misfire seems to have gone completely, but still coming to a junction, usually coasting to a junction causes the engine to stall, so the problems seem to be two fold, maybe I need to look at the MAF sensor next?

Well the Garage fitted new HT leads and a single coil pack, vehicle seems to have developed several more Horses under the Bonnet, kick down does not cause an eml light to appear any longer, the misfire seems to have gone completely, but still coming to a junction, usually coasting to a junction causes the engine to stall, so the problems seem to be two fold, maybe I need to look at the MAF sensor next?

Dale

Depends if thats on Gas or Petrol or both - if its only on gas then it probably needs the calibration doing to sort it.

Bear in mind that it will take some time to clear any trims learnt from the faulty leads etc so driving it on petrol for a short time to monitor what its doing there would be a sensible start anyway.

Well the Garage fitted new HT leads and a single coil pack, vehicle seems to have developed several more Horses under the Bonnet, kick down does not cause an eml light to appear any longer, the misfire seems to have gone completely, but still coming to a junction, usually coasting to a junction causes the engine to stall, so the problems seem to be two fold, maybe I need to look at the MAF sensor next?

Dale

Depends if thats on Gas or Petrol or both - if its only on gas then it probably needs the calibration doing to sort it.

Bear in mind that it will take some time to clear any trims learnt from the faulty leads etc so driving it on petrol for a short time to monitor what its doing there would be a sensible start anyway.

Well I drove all weekend and yesterday covered around 350 miles with on off rough running and stalling at junctions still present although gradually less so, and then on a run today coming to junctions it was clear that rough running and stalling at junctions was just not happening any longer? has the LPG ECU reset itself and began to run correctly now that the HT Leads and Coil Pack have been changed?

Ignition faults are more obvious on lpg than petrol. It does sound like you have it sorted out though no guarantee how well the mapping has been done.

The easiest way to tell is monitor what the swap between fuels is like. It should be smooth if all is well. To tell much more you need more info to work with.

If you have diagnostics for the engine it might be in idea to clear any codes and monitor if any reappear.

It does sound like you've found the main source of the issues though, if it ran well when first converted then it should be ok now.

Well covered a few more hundred miles since the HT leads and coil pack where change, its actually still doing the running rough but again only now and again when I brake to a stop at junctions, really odd, I came down a quite steep hill and to the junction at the bottom and again the engine seemed to be stuttering and rocking the car for a few seconds then it fades away, so its not entirely gone but its not stalling any longer not yet anyway?

Ignition faults are more obvious on lpg than petrol. It does sound like you have it sorted out though no guarantee how well the mapping has been done.

The easiest way to tell is monitor what the swap between fuels is like. It should be smooth if all is well. To tell much more you need more info to work with.

If you have diagnostics for the engine it might be in idea to clear any codes and monitor if any reappear.

It does sound like you've found the main source of the issues though, if it ran well when first converted then it should be ok now.

Well covered a few more hundred miles since the HT leads and coil pack where change, its actually still doing the running rough but again only now and again when I brake to a stop at junctions, really odd, I came down a quite steep hill and to the junction at the bottom and again the engine seemed to be stuttering and rocking the car for a few seconds then it fades away, so its not entirely gone but its not stalling any longer not yet anyway?

I'd say you need to get the calibration/installation looked at now - either the way its been installed is causing the issue (position of nozzles for example) or its just not calibrated correctly. Given it runs OK on petrol when its been run on it for a bit now that suggests trims are drifting. It may be worth either posting some pictures of the install up to check theres nothing obvious wrong there or if you have access to the calibration software to post some screenshots from that. Though if you want to learn while getting it fixed running it into Simon would probably be your best option?

Ignition faults are more obvious on lpg than petrol. It does sound like you have it sorted out though no guarantee how well the mapping has been done.

The easiest way to tell is monitor what the swap between fuels is like. It should be smooth if all is well. To tell much more you need more info to work with.

If you have diagnostics for the engine it might be in idea to clear any codes and monitor if any reappear.

It does sound like you've found the main source of the issues though, if it ran well when first converted then it should be ok now.

Well covered a few more hundred miles since the HT leads and coil pack where change, its actually still doing the running rough but again only now and again when I brake to a stop at junctions, really odd, I came down a quite steep hill and to the junction at the bottom and again the engine seemed to be stuttering and rocking the car for a few seconds then it fades away, so its not entirely gone but its not stalling any longer not yet anyway?

I'd say you need to get the calibration/installation looked at now - either the way its been installed is causing the issue (position of nozzles for example) or its just not calibrated correctly. Given it runs OK on petrol when its been run on it for a bit now that suggests trims are drifting. It may be worth either posting some pictures of the install up to check theres nothing obvious wrong there or if you have access to the calibration software to post some screenshots from that. Though if you want to learn while getting it fixed running it into Simon would probably be your best option?

Does your model S320 have 2 plugs per cylinder? 2 Plugs per cylinder make it far less likely that a misfire will occur, but when a misfire does occur the engine management is very quick to pick up on it and turn off all fuelling to the affected cylinder...

An issue with compromised fuelling can make the mixture in cylinders more difficult to ignite, so a slightly compromised ignition system that might work OK with correct mixture might not work properly with compromised fuelling. Under these conditions there would be 2 problems but sorting either problem could regain proper engine function.

A common mistake that installers of certain branded systems make is to not ensure LPG injector minimum pulse duration is above the minimum at which the injectors will work properly, this can cause the type of symptoms you're seeing, as can calibration issues, as can install issues such as too long pipe lengths or injector channel routing.

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